Hi

In signal chain view (i.e. where you have a graphic of the individual FX, split, mixer amps etc.... - press View several times to see this if it's not already in place), press and hold Enter which should put you into Footswitch Assign mode.  Navigate left and right through all your FX using the 4 way switch to the right of the LCD panel.  Change footswitch assignments by dialing in what you want using the first encoder knob under the LCD.  Return to normal view by pressing View when done.  Save and name your preset in the normal way.  In the blank presets you'll find that some footswitches have already been pre-allocated to FX slots - even empty ones, and this can cause problems with the LED showing up if a footswitch is allocated to a populated FX slot at the same time it's allocated to an un-populated FX slot.  You can assign several FX slots/amp slots to a single foot switch.

Nick